There is plenty of fiat on bitfinex, but often its better to lend it (I lend my fiat reserves for 2days at a time) than have it sitting doing nothing in an order book. I believe this is why the bid side on finex is often thin, especially at any significant distance from the current price.
Just for the record "This Bitfinex Credit Bubble could/might end well".
so there...
but how can we distinguish between fiat that's there to buy in and fiat that will stay lending? some are there only to lend, i am sure.
It's not black and white. If BTC prices on Bitfinex fell 30% below other exchanges, a lot of lenders would use their fiat to buy BTC as soon as their swaps expire.